Electronic devices used with wireless communication systems, such as cellular phones, GPS receivers, and Wi-Fi enabled notebook and tablet computers, generally contain signal processing systems that have interfaces to the analog world. Such interfaces may include wire line and wireless receivers that receive transmitted power and convert the received power to an analog or digital signal that may be demodulated using analog or digital signal processing techniques. A typical wireless receiver architecture includes a low noise amplifier (LNA) that amplifies the very small signals that may be received by an antenna, provides gain to these small signals and passes an amplified signal to later amplification and/or signal processing stages. By providing gain at the LNA, subsequent gain processing stages are made insensitive to noise, thereby enabling a lower system noise figure.
An LNA circuit generally contains at least one transistor and an input matching network. The purpose of the input matching network, which may be made of one or more passive devices such as inductors and capacitors, is to provide an impedance match and/or a noise match to a previous stage, such as an antenna, a filter, an RF switch, or other circuit. LNA implementations may also include an output matching network, a bias network, and other circuit structures such as a cascode transistor.
As wireless RF devices are being used in more environments with more varied specifications, the signal path from antenna system to processing circuit is of increasing importance. Particularly, the placement and usage of LNAs in such varied and demanding systems present varied challenges. Among other things, challenging aspects of designing modern wireless RF devices may include reducing the effects of attenuation, decreasing sensitivity to noise, reducing cost, reducing design time and challenge, and increasing system data rates. These challenges, which often are conflicting or mutually exclusive, present opportunities for improved LNA circuits and system configurations.